Abstract: The invention provides a target object detection system, comprising a plurality of sensing nodes (10) for positioning at respective detection locations with respect to a detection area (12) that is situated within a field generated by an ambient AC source of excitation. Each sensing node has at least one electric potential sensor (22, 42) designed to detect perturbations in said field caused by a target object (14), said one sensor including an electrode (20, 40) responsive to the AC excitation field for generating detection signals, an amplifier (28) connected to the electrode for receiving and amplifying the detection signals to produce AC measurement signals as output, and at least one feedback circuit (30, 36) from an output of the amplifier to an input thereof for enhancing the input impedance of the amplifier.

Abstract: The invention provides a method and apparatus for the detection of charge density distribution at the surface of a material sample. The apparatus comprises an electric potential sensor for measuring surface charge on a material sample, wherein the electrical potential sensor includes a probe for capacitively coupling the electric potential sensor to the surface of the material sample, an amplifier for generating a measurement output, the probe being connected to an input of the amplifier and the measurement output being supplied at an output of the amplifier, and a feedback arrangement driven from the output of the amplifier for enhancing the input impedance of the amplifier.